Microcapsule composition for electrophoretic displays

ABSTRACT

The present invention provides: a microcapsule composition for electrophoretic displays; a production process for the microcapsule composition for the electrophoretic displays; a production process for a sheet for the electrophoretic displays; and a handling method for microcapsules for the electrophoretic displays; wherein the microcapsule composition contains microcapsules and, when used for the electrophoretic displays, can make them as excellent as conventional in various performances (e.g. longtime stability of displaying, respondability of displaying, contrast, and number of times of display rewritability) and, particularly above all, can make the electrophoretic displays exhibit a very high performance as to the contrast. The present invention composition is a composition used for preparation of a coating liquid and comprises an aqueous medium and microcapsules for the electrophoretic displays, wherein the microcapsules include a shell and a dispersion that is capsuled in the shell, wherein the dispersion includes a solvent and electrophoretic fine particles that are dispersed in the solvent; with the composition being characterized by: being a product as obtained without involving the step of drying the microcapsules; and having a microcapsule content of 30 to 80 weight %.

This application is a divisional application of Ser. No. 10/611,934,filed Jul. 3, 2003.

BACKGROUND OF THE INVENTION

A. Technical Field

The present invention relates to: a microcapsule composition forelectrophoretic displays; a production process for the microcapsulecomposition for the electrophoretic displays; a production process for asheet for the electrophoretic displays; and a handling method formicrocapsules for the electrophoretic displays.

B. Background Art

Electrophoretic displays are non-light-emitting type display deviceswhich utilize electrophoretic phenomena of pigment particles in adispersion including a colored solvent and electrophoretic pigmentparticles that are dispersed in the solvent. The electrophoreticdisplays have many excellent properties, such as wide visual-sightangle, longtime memorizability without supply of electric power, and lowconsumption of electric power. Particularly above all, notice is drawnto microcapsules having a structure such that the above dispersion issealed in a capsule shell to be a partition material (for example, referto Japanese Patent No. 2551783), because such microcapsules are usefulfor obtaining display devices having flexibility further in addition tothe above properties. There is expected further technical developmentinto fields of so-called digital papers (e.g. paper-like displays andrewritable papers).

By the way, as to the electrophoretic displays using the microcapsuleswhich are mentioned above as the display devices to which notice isdrawn in recent years, indeed there might have been seen greatenhancements in various functions such as longtime stability ofdisplaying, respondability, contrast, and number of times of displayrewritability, when compared with conventional electrophoretic displayswithout any microcapsule. However, the realization of furtherenhancement of the above various functions is in demand for making thedisplays utilizable universally for various uses as the displayingdevices in the future and also for producing various applied examples.Particularly above all, as to the contrast that has a great influenceupon image vividness, it is strongly desired to further enhance itsperformance.

SUMMARY OF THE INVENTION

A. Object of the Invention

An object of the present invention is to provide: a microcapsulecomposition for electrophoretic displays; a production process for themicrocapsule composition for the electrophoretic displays; a productionprocess for a sheet for the electrophoretic displays; and a handlingmethod for microcapsules for the electrophoretic displays; wherein themicrocapsule composition contains microcapsules and, when used for theelectrophoretic displays, can make them as excellent as conventional invarious performances (e.g. longtime stability of displaying,respondability of displaying, contrast, and number of times of displayrewritability) and, particularly above all, can make the electrophoreticdisplays exhibit a very high performance as to the contrast.

B. Disclosure of the Invention

The present inventors diligently studied to solve the above-mentionedproblems.

As a result, they have thought what influence will be exercised on themicrocapsules themselves in stages of various treatments as required forusing the microcapsules actually as constitutional elements of theelectrophoretic displays should be newly studied in consideration alsofrom the viewpoint of such as performances of the resultant displays.The reasons for this thought are as follows. Making mention of studieswhich have hitherto be made about the microcapsules for theelectrophoretic displays, almost all of them are studies aboutelectrophoretic fine particles to be sealed into the microcapsules and adispersion including the electrophoretic fine particles or aboutconstitutional elements and physical structures of the microcapsules,and there has been no especial study about, when the microcapsules asonce prepared by sealing the dispersion in so as to form the capsulesare thereafter actually used as constitutional elements of theelectrophoretic displays, then what influence the various treatments asmeanwhile carried out will exercise on the microcapsules themselves andfurther on performances of the displays using the microcapsules.

Thus, the present inventors have actually repeated various experimentsand studies. As a result, they have noticed that there are some problemsand points to be improved.

Specifically, the microcapsules have hitherto been processed by thefollowing steps. In the case where the microcapsules have been preparedby microcapsulation in a liquid phase such as an aqueous medium, themicrocapsules are thereafter removed by separating only themicrocapsules from the resultant preparation liquid after the abovepreparation, and then subjected to such as drying to thereby form theminto a finely particulate powder, or the above preparation liquid issubjected to such as centrifugal separation to thereby remove a majorproportion of the liquid to thus isolate the microcapsules (for example,refer to WO 00/20922). In addition, in the case where the microcapsuleshave been prepared by microcapsulation in a gas phase, usually themicrocapsules are thereafter recovered as they are, and then subjectedto such as drying to thereby form them into a finely particulate powder.Then, both in the above cases, the microcapsules which are in such astate as dried are thereafter treated such as by classification when theoccasion demands, and then mixed and dispersed into a predeterminedbinder to thereby form them into a paint. Thereafter this paint iscoated onto such as electrode sheets to thus provide the microcapsulesto the displays.

However, when the isolated microcapsules which are in such a state asdried are mixed and dispersed into the binder, a dispersed state whichis uniform to a certain extent is desired. However, too much power isnecessary for actually dispersing the microcapsules in such a way. Thecause is such that the microcapsules are once put in such a state asdried, and that much aggregation (secondary aggregation) takes place.Then, the present inventors have found that: too much power as abovecauses an excessive load onto the microcapsules; and, after all, in thestage when the microcapsules have finally been provided to the displays,unimaginably many of the microcapsules have already been destroyed. As aresult, all such damage to the microcapsules is a cause of hindering theenhancement of the contrast.

Based on such findings, the present inventors further studied. As aresult, they have thought out a microcapsule composition in which themicrocapsules are allowed to coexist with a considerably large quantityof aqueous medium in order to put the microcapsules to use for theelectrophoretic displays without carrying out an operation such as ofdirectly mixing the binder with the isolated microcapsules themselveswhich are in such a state as dried. That is to say, the presentinventors have thought that: the microcapsules should be used forpreparation of a coating liquid in the form of a composition such thatthe surfaces of the microcapsules are put in a state sufficiently wettedwith the considerably large quantity of aqueous medium; and such acomposition is a novel form that has actually never existed; and thisform would be a clue to direct solution of the problems. Then, thepresent inventors have further found out that the content of themicrocapsules in the composition should be limited into a specificrange. That is to say, the present inventors have found out that: ifsuch a microcapsule composition is used for the preparation of thecoating liquid, the prior art problems can be solved at a stroke.

In addition, the present inventors have found that: in the case wherethe microcapsulation is carried out in a liquid phase such as an aqueousmedium to prepare the microcapsules, if as conventional themicrocapsules are separated from the prepared mixture liquid(preparation liquid) and thereafter dried, then not only does it takelabor and costs, but also the microcapsules, as originally prepared soas to have softness to a certain extent, easily adhere to each otherwhen once dried, so that much aggregation (secondary aggregation)inevitably takes place. Then, the aggregation (secondary aggregation) ofthe microcapsules more easily proceeds because of such as generation ofstatic electricity in the subsequent dry classification apparatus, andthe accuracy of the classification is extremely difficult to enhance.Furthermore, in the case of the dry classification, the friction orshock is directly applied to the microcapsule surfaces, and it istherefore inevitable for the microcapsule to be damaged to a certainextent. The present inventors have guessed that: considerably much ofthe destruction or damage of the microcapsules in the stage when themicrocapsules have been provided to the displays is caused by the abovedamage during the dry classification. In addition, if the classificationof the microcapsules is carried out by the dry classification, theachievement of a high accurate classification is hindered by thedifference in specific gravity between the microcapsules and a gas or byan influence of the cohesive strength due to such as electrostatic forceand van der Waals force. As a result, all of such deterioration of theclassification accuracy and the above damage to the microcapsules is acause of hindering the enhancement of the contrast.

As a method for obtaining the aforementioned microcapsule composition(to which the present inventors have hereupon directed their attention)in a state more optimum for putting this composition to use for theelectrophoretic displays, the present inventors have thought out, on thebasis of the above findings, a method in which the microcapsulecomposition comprising the microcapsules and the aqueous medium isobtained by subjecting the microcapsule composition to necessarytreatment (e.g. classification) in a state of the above-mentionedprepared preparation liquid including the microcapsules and the aqueousmedium. Specifically, the present inventors have guessed that theclassification treatment of the microcapsules should be applied eitherto the above-mentioned prepared preparation liquid itself including themicrocapsules and the aqueous medium or to such as a dilution of thispreparation liquid. Because the classification treatment is applied tothe preparation liquid, it inevitably follows that the classification iscarried out in a wet manner. However, because such as separation anddrying of the microcapsules are not carried out as conventional andbecause the classification is not the dry classification, theclassification of the microcapsules can be carried out with goodaccuracy, and further it is also possible to greatly reduce the damageto the microcapsules.

In addition, the microcapsule content is usually very low in the abovestate of the preparation liquid just after the above preparation. In thecase where a coating liquid is prepared from such a preparation liquidand then used for the electrophoretic displays, not only is itimpossible to provide the microcapsules to the electrophoretic displaysat an appropriate density, but also the coating liquid has such anexcessively low solid content as to be difficult to utilize. Therefore,conventionally, the microcapsules are once isolated from the preparationliquid and then mixed with a binder in a state of dried particles insuch an amount that the concentration will be a desirable value.However, the present inventors have thought that: if the abovepreparation liquid is subjected to treatment of reducing the amount ofthe aqueous medium (so-called concentration treatment), then the aboveproblems can be solved. In addition, the present inventors have thoughtthat it is favorable to carry out the concentration treatment to such anextent that the content of the microcapsules in the composition will bein a specific range. If the microcapsule composition as obtained in thisway is used for the preparation of the coating liquid, then themicrocapsules can be mixed and dispersed very easily and uniformly, andfurther the above-mentioned damage to the microcapsules can effectivelybe inhibited (the amount of the damaged microcapsules can greatly bereduced). In addition, it is also possible to provide theelectrophoretic displays with the microcapsules dispersed at anappropriate density, and therefore the microcapsule composition isexcellent also in a sense of aptitude for the use for theelectrophoretic displays. As a result, various performances (e.g.contrast and image quality of the electrophoretic displays) can greatlybe enhanced. That is to say, the present inventors have thought that, ifin the above way the microcapsule composition having a microcapsulecontent in a specific range is prepared from the above preparationliquid (favorably by subjecting this preparation liquid to theclassification in a wet manner and to the concentration of reducing theaqueous medium) after the preparation of the microcapsules, then theabove effects are all actualized and the aforementioned problems can besolved at a stroke.

Furthermore, the present inventors have found out a handling method formicrocapsules, in which the custody, preservation, transportation, andother various handling of the microcapsules are carried out in theoptimum state so that more excellent electrophoretic displays can beobtained when the microcapsules as prepared by the microcapsulation byvarious production processes in a liquid phase or gas phase are used forthe electrophoretic displays. Specifically, the present inventors havethought that the prepared microcapsules should be handled in the form ofthe composition in which the microcapsules are allowed to coexist withthe aqueous medium. In addition, the present inventors have furtherfound out that the microcapsule content in the above composition shouldbe in a specific range. The same effects as those of the microcapsulecomposition as obtained by the above production process can be obtainedby handling the microcapsules in this way.

Furthermore, the present inventors have completed a production processfor a sheet for electrophoretic displays as usage of the presentinvention microcapsule composition.

That is to say, a microcapsule composition for electrophoretic displays,according to the present invention, is a composition used forpreparation of a coating liquid and comprises an aqueous medium andmicrocapsules for the electrophoretic displays, wherein themicrocapsules include a shell and a dispersion that is capsuled in theshell, wherein the dispersion includes a solvent and electrophoreticfine particles that are dispersed in the solvent; with the microcapsulecomposition being characterized by: being a product as obtained withoutinvolving the step of drying the microcapsules; and having amicrocapsule content of 30 to 80 weight %.

In the present invention microcapsule composition for theelectrophoretic displays, it is favorable that the microcapsules have avolume-average particle diameter of 30 to 150 μm and a particle diameterdistribution by volume such that: not less than 80 volume % of themicrocapsules are present within the particle diameter range of ±40% ofthe maximum-peak particle diameter around the maximum-peak particlediameter.

In the present invention microcapsule composition for theelectrophoretic displays, it is favorable that the total content of themicrocapsules and the aqueous medium in the composition is not less than90 weight %.

A production process for the microcapsule composition for theelectrophoretic displays, according to the present invention, is aproduction process for the microcapsule composition including an aqueousmedium and microcapsules for the electrophoretic displays, wherein themicrocapsules include a shell and a dispersion that is capsuled in theshell, wherein the dispersion includes a solvent and electrophoreticfine particles that are dispersed in the solvent; with the productionprocess being characterized by comprising: the dispersing step ofdispersing the electrophoretic fine particles into the solvent; and themicrocapsuling step of capsuling an electrophoretic fine particledispersion into the shell in the presence of the aqueous medium, therebyobtaining a preparation liquid including the microcapsules and theaqueous medium, wherein the electrophoretic fine particle dispersion isobtained in the dispersing step; with the production process furtherbeing characterized in that: the composition having a microcapsulecontent of 30 to 80 weight % is obtained without involving the step ofdrying the microcapsules.

In the present invention production process for the microcapsulecomposition for the electrophoretic displays, it is favorable that thisprocess further comprises: the wet classification step of treating thepreparation liquid to classify the microcapsules; and the concentrationstep of reducing the aqueous medium from a dispersion resultant from theclassification step, thereby concentrating the dispersion.

In the present invention production process for the microcapsulecomposition for the electrophoretic displays, it is favorable that thepreparation liquid to be used in the wet classification step has amicrocapsule concentration of not more than 15 weight %.

A production process for a sheet for the electrophoretic displays,according to the present invention, comprises the steps of: coating acoating liquid containing a microcapsule composition for theelectrophoretic displays; and drying the resultant coating film; therebyproducing the sheet for the electrophoretic displays; with theproduction process being characterized by: using, as the composition,the above present invention microcapsule composition for theelectrophoretic displays; and further comprising the step of preparingthe coating liquid by mixing the composition in such an amount that thecoating liquid will have a microcapsule content of 25 to 65 weight %.

A handling method for microcapsules for the electrophoretic displays,according to the present invention, is a handling method for themicrocapsules including a shell and a dispersion that is capsuled in theshell, wherein the dispersion includes a solvent and electrophoreticfine particles that are dispersed in the solvent. This handling methodis characterized in that the microcapsules are handled in the form of amicrocapsule composition such that: the microcapsules are present in anaqueous medium; and the microcapsule composition has a microcapsulecontent of 30 to 80 weight %.

These and other objects and the advantages of the present invention willbe more fully apparent from the following detailed disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, detailed descriptions are specifically given about thepresent invention microcapsule composition for the electrophoreticdisplays, the present invention production process for the microcapsulecomposition for the electrophoretic displays, the present inventionproduction process for the sheet for the electrophoretic displays, andthe present invention handling method for the microcapsules for theelectrophoretic displays. However, the scope of the present invention isnot bound to these descriptions in any way. And other than the followingillustrations can also be carried out appropriately within the scope notdeparting from the spirit of the present invention.

The present invention production process for the microcapsulecomposition for the electrophoretic displays (which may hereinafter bereferred to as the present invention production process for thecomposition) is a production process for the microcapsule compositionincluding an aqueous medium and microcapsules for the electrophoreticdisplays, wherein the microcapsules include a shell and a dispersionthat is capsuled in the shell, wherein the dispersion includes a solventand electrophoretic fine particles that are dispersed in the solvent.This production process is characterized by comprising thebelow-mentioned dispersing step and microcapsuling step and furthercharacterized in that: the composition having a microcapsule content of30 to 80 weight % is obtained without involving the step of drying themicrocapsules.

In the present invention, the dispersing step is a step of dispersingthe electrophoretic fine particles into the solvent. The dispersingliquid resultant from this step is a dispersion to be finally capsuledin the microcapsules for the electrophoretic displays.

The solvent will do if it is a solvent having hitherto been usedconventionally and generally for dispersions for the electrophoreticdisplays. Therefore, the solvent is not especially limited.High-insulating organic solvents are favorable.

Favorable examples of the high-insulating organic solvents include onemember alone or mixtures selected from the group consisting of: aromatichydrocarbons, such as o-, m-, or p-xylene, toluene, benzene,dodecylbenzene, hexylbenzene, phenylxylylethane, and naphthenichydrocarbons; aliphatic hydrocarbons, such as cyclohexane, n-hexane,kerosine, and paraffinic hydrocarbons; various esters, such as ethylacetate and butyl acetate; ketones, such as acetone, methyl ethylketone, and methyl isobutyl ketone; alcoholic solvents, such asmethanol, ethanol, isopropanol, octanol, and methyl cellosolve;halogenated hydrocarbons, such as chlorobutane, chloroform,trichloroethylene, trichlorofluoroethylene, trichloroethane, carbontetrachloride, cyclohexyl chloride, chlorobenzene,1,1,2,2-tetrachloroethylene, trichlorofluoroethane,tetrafluorodibromoethane, bromoethane, tetrafluorodifluoroethane,methylene iodide, triiodosilane, and methyl iodide; and carbondisulfide. Of the above, such as long-chain-alkylbenzenes (e.g.dodecylbenzene and hexylbenzene) and phenylxylylethane are morefavorable because they have a high boiling point and also a high flashpoint, and further have almost no toxicity. These solvents may be usedeither alone respectively or in combinations with each other.

The amount of the solvent as used is favorably adjusted so as to be inthe range of 40 to 95 weight %, more favorably 50 to 92 weight %, stillmore favorably 60 to 90 weight %, relative to the entire dispersion asobtained. In the case where the above amount is smaller than 40 weight%, the viscosity of the dispersion rises so much as to lower theelectrophoretic ability of the electrophoretic fine particles. In thecase where the above amount is larger than 95 weight %, theconcentration of the electrophoretic fine particles is so low that thecontrast cannot be obtained sufficiently.

The solvent is favorably a colorless and transparent solvent, and may,for example, get colored when the occasion demands.

In the case where the solvent is a colored one, there is no especiallimitation on the dye used for the coloring. However, oil-soluble dyesare favorable, and such as azo dyes and anthraquinone dyes are morefavorable particularly in respect of being easy to use. Specificfavorable examples thereof include: as yellow dyes, azo compounds (e.g.Oil Yellow 3G (produced by Orient Chemical Co., Ltd.)); as yellowishbrown dyes, azo compounds (e.g. Fast Orange G (produced by BASF)); asblue dyes, anthraquinones (e.g. Macrorex Blue RR (produced by Bayer));as green dyes, anthraquinones (e.g. Sumiplast Green G (produced bySumitomo Chemical Co., Ltd.)); as brown dyes, azo compounds (e.g. OilBrown GR (produced by Orient Chemical Co., Ltd.)); as red dyes, azocompounds (e.g. Oil Red 5303 (produced by Arimoto Chemical Co., Ltd.)and Oil Red 5B (produced by Orient Chemical Co., Ltd.)); as purple dyes,anthraquinones (e.g. Oil Violet #730 (produced by Orient Chemical Co.,Ltd.)); as black dyes, azo compounds (e.g. Sudan Black X60 (produced byBASF); and mixtures of Macrorex Blue FR as an anthraquinone (produced byBayer) and Oil Red XO as an azo compound (produced by Kanto ChemicalCo., Ltd.). These dyes may be used either alone respectively or incombinations with each other.

The above dye is usually used in an amount of favorably 0.1 to 10 partsby weight, more favorably 0.5 to 10 parts by weight, still morefavorably 1 to 10 parts by weight, per 100 parts by weight of thesolvent. In the case where the amount of the above dye as used issmaller than 0.1 part by weight, the coloring ability is so insufficientthat the contrast to the electrophoretic fine particles cannotsufficiently be obtained. In the case where the above amount is largerthan 10 parts by weight, the costs increase more than is necessary.

The electrophoretic fine particles will do if they are electrophoreticpigment particles, namely, colored particles that display plus or minuspolarity in the dispersion. Although there is no especial limitation ontheir kinds, specifically there are favorably used such as whiteparticles (e.g. Titanium Oxide) and black particles (e.g. Carbon Blackand Titanium Black), and there may also be used other particles asmentioned below. These may be used either alone respectively or incombinations with each other.

In the case of using the fine particles of the titanium oxide, there isno especial limitation on the kind of the titanium oxide. That will doif it is titanium oxide as generally used as a white pigment, and thetitanium oxide may be either a rutile type or anatase type. However, inthe case of considering such as discoloration of colorants due tophotoactive performance of the titanium oxide, the rutile type titaniumoxide displaying low photoactive performance is favorable, and there ismore favorable titanium oxide as processed by such as Si treatment, Altreatment, Si—Al treatment, or Zn—Al treatment for further lowering thephotoactive performance.

As the electrophoretic fine particles, other particles besides the abovefine titanium oxide particles, Carbon Black, and Titanium Black may beused together, and the above other particles may be used instead of suchas the titanium oxide. The above other particles are, favorably, pigmentparticles similarly to such as the fine titanium oxide particles. Inaddition, there is not always necessity for the above other particles tohave the electrophoretic ability similarly to such as the fine titaniumoxide particles. If necessary, the electrophoretic ability may be givenby some hitherto publicly known method.

Although there is no especial limitation on the above other particles,specific favorable examples thereof include: as white particles otherthan the above titanium oxide, inorganic pigments (e.g. Barium Sulfate,Zinc Oxide, and Zinc White); as yellow particles, inorganic pigments(e.g. Yellow Iron Oxide, Cadmium Yellow, Titanium Yellow, and ChromeYellow) and organic pigments, such as insoluble azo compounds (e.g. FastYellow), condensed azo compounds (e.g. Chromophthal Yellow), azo complexsalts (e.g. Benzimidazolone Azo Yellow), condensed polycyclics (e.g.Flavans Yellow), Hansa Yellow, naphthol yellow, nitro compounds, andpigment yellow; as yellowish brown particles, inorganic pigments (e.g.Molybdate Orange) and organic pigments, such as azo complex salts (e.g.Benzimidazolone Azo Orange) and condensed polycyclics (e.g. PelinonOrange); as red particles, inorganic pigments (e.g. Ferric Oxide Red andCadmium Red) and organic pigments, such as dyeing lakes (e.g. MadderLake), soluble azo compounds (e.g. Lake Red), insoluble azo compounds(e.g. naphthol red), condensed azo compounds, (e.g. ChromophthaloScarlet Red), condensed polycyclics (e.g. Tioindigo Voldor),quinacridone pigments (e.g. Cinquasia Red Y and Fastpermanent Red), andazo pigments (e.g. Permanent Red and Fast Slow Red); as purpleparticles, inorganic pigments (e.g. Manganese Violet) and organicpigments, such as dyeing lakes (e.g. Rhodamine Lake) and condensedpolycyclics (e.g. Dioxadine Violet); as blue particles, inorganicpigments (e.g. Iron Blue, Ultramarine, Cobalt Blue, and Cerlian Blue)and organic pigments, such as phthalocyanines (e.g. PhthalocyanineBlue), indanthrenes (e.g. Indanthrene Blue), and alkali blue; as greenparticles, inorganic pigments (e.g. Emerald Green, Chrome Green,Chromium Oxide, and Viridian) and organic pigments, such as azo complexsalts (e.g. Nickel Azo Yellow), nitroso compounds (e.g. Pigment Greenand Naphthol Green), and phthalocyanines (e.g. Phthalocyanine Green);and as black particles other than the above Carbon Black and TitaniumBlack, inorganic pigments (e.g. Iron Black) and organic pigments (e.g.Aniline Black). These may be used either alone respectively or incombinations with each other.

Although there is no especial limitation on the particle diameters ofthe electrophoretic fine particles, their volume-average particlediameter is favorably in the range of 0.1 to 5 μm, more favorably 0.2 to3 μm. In the case where the above particle diameter (volume-averageparticle diameter) is smaller than 0.1 μm, there is a possibility that:the hiding performance is not sufficiently obtained in a displayingportion of the electrophoretic displays, so that the coloring degree islowered, and there cannot be obtained electrophoretic displays havinghigh contrast. In the case where the above particle diameter is largerthan 5 μm, there is a possibility that there may occur necessity toraise the coloring degree of the particles themselves (the pigmentconcentration) more than is necessary, and besides, there is also apossibility that the smooth electrophoretic property of the fineparticles may be lowered.

The concentration of the electrophoretic fine particles in thedispersion is favorably in the range of 5 to 60 weight %, more favorably5 to 50 weight %, still more favorably 5 to 40 weight %. In the casewhere the above concentration of the electrophoretic fine particles isless than 5 weight %, there is a possibility that: neither the coloringnor the hiding performance is sufficiently exhibited by theelectrophoretic fine particles in a displaying portion of theelectrophoretic displays, so that a sufficient contrast cannot beobtained, and therefore a vivid displaying cannot be obtained. In thecase where the above concentration is more than 60 weight %, there is apossibility that the viscosity during the dispersing treatment may be sohigh as to overload the dispersing apparatus, and besides, there is apossibility of aggregating the electrophoretic fine particles when highenergy is applied to the displaying portion of the electrophoreticdisplays, or there is a possibility that the response rate(respondability of displaying) of the electrophoretic fine particles maybe lowered in a portion to which a voltage is applied.

In the dispersing step, the dispersion as obtained can include someother component besides the above solvent and electrophoretic fineparticles when the occasion demands. However, there is no especiallimitation on such as its kind. Examples of the above other componentinclude dispersants. The dispersants may be included either before orafter the electrophoretic fine particles are dispersed into the solvent,and there is no especial limitation.

There is no especial limitation on the above dispersants. Thedispersants will do if they are dispersants usable conventionally andgenerally for assisting the particles in being dispersed in the solvent.Specific favorable examples thereof include: anionic surfactants solublein the dispersion, cationic surfactants, amphoteric surfactants,nonionic surfactants, fluorosurfactants, sorbitan fatty acid estersurfactants (e.g. sorbitan sesquioleate), dispersants (e.g. blockpolymers and graft polymers), and various coupling agents. These may beused either alone respectively or in combinations with each other. Ofthe above dispersants, the coupling agents are more favorable becausethey also enhance the dispersing stability when the charges are applied.If the fine particles are treated with the coupling agents, a coatinglayer of the coupling agent is formed on surfaces of the fine particles.

There is no especial limitation on the kinds of the above couplingagents. However, favorable examples thereof include: (1) silane couplingagents; (2) titanate coupling agents; (3) aluminum coupling agents; (4)vinyl-group-containing coupling agents; (5) coupling agents containingat least one group selected from among an amino group, a quaternaryammonium salt, a carboxyl group, and a phosphoric acid group; (6)coupling agents containing an amino group or a glycidyl group at theirend; and (7) organosilazanes. The titanate coupling agents and thealuminum coupling agents are more favorable. Coupling agents belongingto the above various coupling agents and also containing a long-chainalkyl group are still more favorable. Titanate coupling agents andaluminum coupling agents also containing a long-chain alkyl group areparticularly favorable. The above coupling agents may be used eitheralone respectively or in combinations with each other.

As is mentioned above, the reason that the coupling agents containing along-chain alkyl group are favorable can be exemplified by such that:the affinity is raised by such as long-chain-alkylbenzenes which arehigh safe solvents, and therefore such coupling agents have high effectsof raising the dispersing stability of the electrophoretic fineparticles.

Although there is no especial limitation on the silane coupling agents,favorable examples thereof include: silane coupling agents containingsuch as a vinyl group, an amino group, a glycidyl group, and a thiolgroup; and silane coupling agents containing a long-chain alkyl group.These may be used either alone respectively or in combinations with eachother.

Although there is no especial limitation on the titanate couplingagents, favorable examples thereof include compounds as represented bythe following general formula (1):(RO)_(m)—Ti—X_(a)  (1)

(where: R denotes an alkyl group having 1 to 4 carbon atoms; X denotesan alkyl group having 8 to 18 carbon atoms, a fatty acid residue, ahydroxyphenyl group, or a hydrocarbon residue; m denotes an integer of 1to 4; and a denotes an integer of 1 to 3). Specific favorable examplesof the titanate coupling agents as represented by the above generalformula (1) include isopropyl.triisostearoyl titanate, isopropyltridecylbenzenesulfonyl titanate,isopropyl.tris(dioctylpyrophosphate)titanate, isopropyl.trioctanoyltitanate, isopropyl.dimethacryl.isostearoyl titanate,isopropyl.diacryl.isostearoyl titanate,isopropyl.tris(dioctylphosphate)titanate, isopropyl.tricumylphenyltitanate, isopropyl.tris(N-aminoethyl)titanate,tetraisopropyl.bis(dioctylphosphite)titanate,tetraoctyl.bis(ditridecylphosphite)titanate,tetra(2,2-diallyloxymethyl-1-butyl).bis(di-tridecyl)phosphite titanate,bis(dioctylpyrophosphate)oxyacetate titanate, dicumylphenyl.oxyacetatetitanate, diisostearoylethylene titanate, andbis(dioctylpyrophosphate)ethylene titanate. Incidentally, these are, forexample, commercially available in the trade name of Plemact fromAjinomoto Co., Inc. These may be used either alone respectively or incombinations with each other.

Although there is no especial limitation on the aluminum couplingagents, favorable examples thereof include hitherto publicly knownvarious aluminum chelates, alkyl acetoacetate aluminum diisopropylate,and aluminum-bis(ethyl acetate)-diisopropylate. These may be used eitheralone respectively or in combinations with each other.

Although there is no especial limitation on the vinyl-group-containingcoupling agents, favorable examples thereof include: alkoxysilanes, suchas vinyltrimethoxysilane and dimethylvinylmethoxysilane; chlorosilanes,such as vinyltrichlorosilane and dimethylchlorosilane;methacryloxysilanes, such as γ-methacryloxypropyltrimethoxysilane andγ-methacryloxypropylmethyldimethoxysilane; quaternary ammonium salts,such as N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane; andtitanates, such as isopropyl dimethacryl isostearoyl titanate andisopropyl diacryl isostearoyl titanate. These may be used either alonerespectively or in combinations with each other.

The coupling agents containing at least one group selected from among anamino group, a quaternary ammonium salt, a carboxyl group, and aphosphoric acid group are charge-donating agents. Although notespecially limited, specific favorable examples thereof include:silanes, such as γ-aminopropyltriethoxysilane andoctadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride;titanates, such as isopropyl triisostearoyl titanate andisopropyl-tris(dioctylpyrophosphate)titanate. These may be used eitheralone respectively or in combinations with each other.

Although there is no especial limitation on the coupling agentscontaining an amino group or a glycidyl group at their end, favorableexamples thereof include: silane coupling agents, such asγ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; andtitanate coupling agents such as isopropyl-tris(N-aminoethyl)titanate.These may be used either alone respectively or in combinations with eachother.

Although there is no especial limitation on the organosilazanes, it isenough that they are hitherto publicly known organosilazane compounds.Favorable examples thereof include compounds represented by thefollowing formulas (a), (b), and (c) as described in JP-A-008637/1988.[(CH₃)₃Si]₂NH  (a)[(C₂H₅)₃Si]₂NH  (b)[(C₃H₇)₃Si]₂NH  (c)

These may be used either alone respectively or in combinations with eachother.

Although there is no especial limitation on the coupling agentscontaining a long-chain alkyl group, favorable examples thereof include:alkoxysilanes, such as propyltrimethoxysilane, butyltrimethoxysilane,hexyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane,hexadecyltrimethoxysilane, and octadecyltrirnethoxysilane;chlorosilanes, such as propyldodecyltrichlorosilane,butyltrichlorosilane, hexyltrichlorosilane, decyltrichlorosilane,dodecyltrichlorosilane, hexadecyltrichlorosilane, andoctadecyltrichlorosilane; fluorosilanes, such astrifluoropropyltrimethoxysilane, trifluoropropyltrichlorosilane,tridecafluorooctyltrimethoxysilane, tridecafluorooctyltrichlorosilane,heptadecafluorodecyltrimethoxysilane, andheptadecafluorodecyltrichlorosilane; and titanates, such as isopropyltriisostearoyl titanate and isopropyl trioctanoyl titanate. Of thesecoupling agents containing a long-chain alkyl group, such as thealkoxysilanes, the chlorosilanes, and the fluorosilanes are morefavorable. These may be used either alone respectively or incombinations with each other.

Although there is no especial limitation on the method for dispersingthe electrophoretic fine particles into the solvent in the dispersingstep, it is enough that this method is a method as conventionally usedwhen desirable particles are dispersed into some solvent. Specificexamples thereof include: a method that involves the steps of chargingan ultrasonic bath with such as the fine titanium oxide particles, thesolvent, and the coupling agent as raw components, and thenultrasonically dispersing the resultant mixture under stirredconditions; a method that involves the step of making a dispersion witha dispersing machine such as a paint shaker, a ball mill, and a sandgrind mill; a dry method that involves the step of, while forciblystirring the solvent and the fine particles with such as a V-blender,spraying the coupling agent thereonto by dry air or nitrogen gas; a wetmethod that involves the steps of properly dispersing the fine particlesinto the solvent to thereby form a slurry, and then adding thereto thecoupling agent; and a spraying method that involves the step of, whilevigorously stirring the preheated solvent and fine particles, sprayingthe coupling agent thereonto.

The microcapsuling step in the present invention is a step of capsulingan electrophoretic fine particle dispersion into the shell (capsuleshell) in the presence of the aqueous medium, wherein theelectrophoretic fine particle dispersion is obtained in theaforementioned dispersing step. The preparation liquid including theaqueous medium and the microcapsules as prepared by the microcapsulationis obtained by this step.

There is no especial limitation on the method for carrying out the abovecapsulation. It is enough that the method for carrying out themicrocapsulation is adopted by appropriately selecting it from amongconventional and publicly known methods. Specific examples thereofinclude so-called interfacial precipitation methods (e.g. a coacervationmethod (phase separation method), a melting-decomposition-coolingmethod, powdery bed method) and so-called interfacial reaction methods(e.g. a interfacial polymerization method, an in-situ method, acoating-film (covering) method by curing in liquids (orifice method),and an interfacial reaction method (inorganochemical reaction method)).Of the above, the coacervation method (phase separation method), thein-situ method, the interfacial polymerization method, and themelting-decomposition-cooling method are more favorable. In thesevarious production processes, the microcapsulation is carried out in thepresence of the aqueous medium, thereby obtaining the preparation liquidincluding the microcapsules and the aqueous medium.

Although there is no especial limitation on the aqueous medium usable inthe above various production processes, specific usable examples thereofinclude: water; mixed liquids of water and hydrophilic solvents (e.g.alcohols, ketones, esters, and glycols); solutions as obtained bydissolving water-soluble polymers (e.g. PVA (polyvinyl alcohol), CMC(carboxymethyl cellulose), gelatins, and gum arabic) into water;solutions as obtained by adding surfactants (e.g. anionic surfactants,cationic surfactants, and nonionic surfactants) to water; or liquids asobtained by combining these aqueous mediums.

Although there is no especial limitation on the amount of the dispersion(obtained in the above dispersing step) to be dispersed into the aqueousmedium, specifically this dispersion is favorably used in an amount of20 to 200 parts by weight, more favorably 30 to 150 parts by weight, per100 parts by weight of the aqueous medium. In the case where the aboveamount is smaller than 20 parts by weight, there is a possibility thatthe resultant microcapsules may have such a broad particle diameterdistribution as to cause the lowering of the production efficiency. Inthe case where the above amount is larger than 200 parts by weight,there is a possibility that: a reversed suspension may be formed, andtherefore the microcapsules cannot be produced.

The raw material of the capsule shell will do if it is the same as usedfor hitherto publicly known microcapsules. Thus, there is no especiallimitation. In the case of using the coacervation method, examples ofraw materials that are favorably used include anionic substances (e.g.gum arabic, sodium alginate, copolymers of styrene-maleic anhydride,copolymers of vinyl methyl ether-maleic anhydride, phthalate esters ofstarch, and polyacrylic acid). In the case of using the in-situ method,examples of raw materials that are favorably used includemelamine-formalin resins (melamine-formalin prepolymers). In the case ofusing the interfacial polymerization method, hydrophilic polymers (e.g.polyamines, glycols, and polyphenols) and hydrophobic polymers (e.g.polybasic acid halides, bisharofolmerl, and polyisocyanates) arefavorably used as the raw materials to form a capsule shell made of suchas polyamides, epoxy resins, polyurethanes, and polyureas.

Such as polyamines may further be added to these raw materials of thecapsule shell, whereby there can be obtained microcapsules having acapsule shell which is excellent in such as heat-resistantpreservability. The amount of such as polyamines to be used will do ifit is to such an extent as not to extremely damage desirable shellproperties derived from the above raw material of the capsule shell.

Favorable examples of the above polyamines include: aliphatic amines,such as ethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, 1,3-propylenediamine, and hexamethylenediamine;epoxy compound addition products from aliphatic polyamines, such aspoly(1 to 5)alkylene(C₂ to C₆)polyamine-alkylene(C₂ to C₁₈) oxideaddition products; aromatic polyamines, such as phenylenediamine,diaminonaphthalene, and xylylenediamine; alicyclic polyamines such aspiperazine; and heterocyclic diamines such as3,9-bis-aminopropyl-2,4,8,10-tetraoxaspiro-[5.5]undecane. These may beused either alone respectively or in combinations with each other.

Although there is no especial limitation on the amount of the rawmaterial of the capsule shell to be used, this amount is specifically inthe range of favorably 1 to 50 parts by weight, more favorably 5 to 30parts by weight, per 1 part by weight of the electrophoretic fineparticle dispersion. In the case where the above amount to be used isoutside the above range, there is a possibility that the below-mentioneddesirable thickness of the capsule shell cannot be obtained.

In the microcapsuling step, when the occasion demands, there can beappropriately used other components besides the above aqueous medium,the above raw material of the capsule shell, and the above dispersion asobtained in the dispersing step.

Although there is no especial limitation on the shape of themicrocapsules as obtained in the microcapsuling step, it is favorable toappropriately set conditions in such a manner that the microcapsuleswill be the shape of particles such as true spheres.

Although there is no especial limitation on the volume-average particlediameter of the microcapsules as obtained in the microcapsuling step,specifically it is favorable to appropriately set conditions (e.g.diameters of particles dispersed in the dispersion) in such a mannerthat the above volume-average particle diameter will be in the range of5 to 300 μm, more favorably 10 to 200 μm, still more favorably 15 to 150μm. In the case where the volume-average particle diameter of themicrocapsules is smaller than 5 μm, there is a possibility that: whenthe microcapsules are put to use for the electrophoretic displays, thedisplaying concentration cannot sufficiently be obtained in thedisplaying portion of the electrophoretic displays. In the case wherethe volume-average particle diameter of the microcapsules is larger than300 μm, there is a possibility that there may occur problems in themechanical strength of the microcapsules themselves, and besides, thereis a possibility that: when the microcapsules are put to use for theelectrophoretic displays, the electrophoretic properties of such as thefine titanium oxide particles in the dispersion as sealed in themicrocapsules may not sufficiently be displayed, and the staring voltagefor displaying may also increase.

Although there is no especial limitation on the thickness of the capsuleshell of the microcapsules as obtained in the microcapsuling step,specifically it is favorable to appropriately set conditions (e.g. theamount of the raw material of the capsule shell to be used) in such amanner that the above thickness will be in the range of 0.1 to 5 μm,more favorably 0.1 to 4 μm, still more favorably 0.1 to 3 μm. In thecase where the thickness of the capsule shell is less than 0.1 μm, thereis a possibility that the strength as the capsule shell may notsufficiently be obtained. In the case where the thickness of the capsuleshell is more than 5 μm, there is a possibility that: the transparencymay be lowered so much as to cause the lowering of the contrast, andbeside, the softness of the microcapsules themselves may be lowered somuch as to result in insufficient adhesion to such as electrode films.

In the present invention production process for the composition, it isimportant that the microcapsule content in the composition as obtainedis adjusted in the range of 30 to 80 weight %, favorably 35 to 80 weight%, more favorably 40 to 70 weight %. In the case where the above contentis less than 30 weight %, there is a possibility that: when thecomposition is formed into a paint, the microcapsule concentration maybecome so low that the microcapsules are difficult to arrange in a layerdensely by the side of each other on a surface to be coated, thusresulting in occurrence of spaces to cause a lack of displaying andtherefore to cause the lowering of the contrast and the image defect(displaying defect). In addition, in the case where the above content ismore than 80 weight %, there is a possibility such that: themicrocapsules may mutually aggregate to cause problems in thedispersibility when the composition is formed into a paint; or the imagedefect (displaying defect) may be caused in the case where themicrocapsules cannot sufficiently be dispersed; or, if the microcapsulesare strongly dispersed, they may be damaged so much that theelectrophoretic fine particle dispersion leaks from inside themicrocapsules due to the pressure as applied by laminating an electrodefilm to be a counter electrode. Because of these problems, the resultantelectrophoretic displays cannot sufficiently obtain the contrast, andhave a lot of image defects (displaying defects).

In the present invention, it is important that: as mentioned above, themicrocapsules to be used for the preparation of the coating liquid areproduced not in the form of the isolated microcapsules which are in sucha state as dried, but in the form of a composition such that thesurfaces of the microcapsules are put in a state sufficiently wettedwith a considerably large quantity of aqueous medium. Such a productionprocess can reduce the labor and costs as needed for separating and thendrying the microcapsules as conventional, and besides, can furtherreduce damage as done to the microcapsules by such as friction or shockaccompanying the drying. Then, for example, as mentioned below, theresultant composition can display excellent effects when used for thepreparation of the coating liquid as it is. Incidentally, in the presentinvention, it is necessary that the microcapsules to be used for thepreparation of the coating liquid are produced in the form of acomposition such that the surfaces of the microcapsules are put in astate sufficiently wetted with a considerably large quantity of aqueousmedium. In addition, from the view point of the labor and costs asneeded for separating and then drying the microcapsules and from theview point of the damage as done to the microcapsules by such asfriction or shock accompanying the drying, it is necessary that theabove composition is produced without involving the step of drying themicrocapsules.

Although there is no especial limitation on the method for adjusting themicrocapsule content in the range of 30 to 80 weight % in thecomposition as obtained, the microcapsule content in the composition isfavorably adjusted in the range of 30 to 80 weight % by carrying out theconcentration step of reducing the aqueous medium. However, in the casewhere the preparation liquid as obtained in the microcapsuling step hasalready been a composition having a microcapsule content of 30 to 80weight %, such as the above concentration step is not necessary to carryout.

The above concentration step may be applied either to the preparationliquid as obtained in the microcapsuling step or to a dispersion asobtained by classification in the below-mentioned wet classificationstep.

The above concentration step is a step in which a treatment of reducingthe amount of the aqueous medium is applied either to the preparationliquid resultant from the microcapsuling step (preparation liquidincluding the prepared microcapsules and the aqueous medium) or to thedispersion as obtained by classification in the below-mentioned wetclassification step. That is to say, the above concentration step is astep of reducing the aqueous medium from the above preparation liquid ordispersion, thereby raising the microcapsule content. Usually in thecase of considering that the composition including the microcapsules andthe aqueous medium is put to use for the electrophoretic displays, thenthe microcapsule concentration is often too low in the preparationliquid as it is after having been obtained by the microcapsuling step.If such a preparation liquid is used as it is, for example, there areproblems in that: when this preparation liquid is put to use in the formmixed into the binder, even if this mixing and the dispersing itself ofthe microcapsules are easy, it is after all impossible to provide themicrocapsules to the electrophoretic displays at a sufficient density,and therefore the product quality is deteriorated. If the aqueous mediumis reduced in the above concentration step in such a manner that themicrocapsule concentration will be in a specific range, then the aboveproblems can easily be solved. In addition, for example, when comparedwith such as a method in which microcapsules as once powdered by dryingare dispersed into the binder, a method in which microcapsules aredispersed by mixing the binder with a concentrate of the abovepreparation liquid can greatly lessen the damage to the microcapsulesand also can easily uniformly disperse the microcapsules.

Favorably, if the concentration step is carried out, then thecomposition including the microcapsules and the aqueous medium isobtained in a state where the microcapsule content is raised to adesirable range. Therefore, the labor, time, and costs for thetransportation, storage, and other handling of the above composition perunit quantity of the microcapsules can be reduced, and besides, it ispossible to achieve the productivity enhancement and the cost reductionas to final products such as the electrophoretic displays.

Although there is no especial limitation on the concentration method,specific examples thereof include a suction filtration method, apressurizing filtration method, a centrifugal sedimentation method, acentrifugal filtration method, and a filter press method.

In the present invention production process for the composition, the wetclassification step is favorably carried out before the aboveconcentration step. In this case, it follows that the aboveconcentration step is applied to a dispersion resultant from theclassification in the wet classification step.

The above wet classification step is a step of carrying out a treatmentof applying the classification of the microcapsules to the preparationliquid resultant from the microcapsuling step, namely, the preparationliquid including the prepared microcapsules and the aqueous medium. Theclassification is wet classification because the above preparationliquid is classified. Specifically, the wet classification step is, forexample, a classification step of carrying out the classificationtreatment of the above preparation liquid either as it is or afterhaving diluted it with such as any aqueous medium, whereby themicrocapsules in the preparation liquid are classified so as to havedesirable particle diameters or a desirable particle diameterdistribution.

The wet classification can be carried out by methods or withapparatuses, which methods and apparatuses involve manners such as asieving manner (filtration manner), a centrifugal sedimentation manner,and a natural sedimentation manner. The sieving manner can effectivelybe used for microcapsules having relatively large particle diameters.

As to the classification in the sieving manner, it is efficient andfavorable to carry out this classification under application ofvibration.

Examples of the classification in the centrifugal sedimentation mannerinclude a batch manner (e.g. bucket type) and a continuous manner (e.g.cyclone type). The classification in the continuous manner is a mannerin which the classification is carried out by utilizing the differencein specific gravity between the microcapsules with a high-speed rotatingstream. This manner can continuously carry out the classification andtherefore enables industrial mass production.

As to such a wet classification, it is favorable, for solving problemssuch as of mutual aggregation of particles and clogging, that theclassification operation is carried in a state where the microcapsuleparticle concentration is low in the preparation liquid. This particleconcentration is favorably not more than 15 weight %, more favorably notmore than 10 weight %, still more favorably not more than 5 weight %.

In order that the microcapsule particle concentration in the preparationliquid during the wet classification step can be in the above-mentionedlow range, when the occasion demands, the preparation liquid may bediluted by adding thereto the aqueous medium before the wetclassification step.

The present invention production process for the composition may furthercomprise other steps besides the above various steps when the occasiondemands. Examples thereof include a step of washing the microcapsules.

The present invention microcapsule composition for the electrophoreticdisplays (which may hereinafter be referred to as the present inventionmicrocapsule composition or as the present invention composition) is acomposition used for the preparation of the coating liquid and comprisesthe aqueous medium and the microcapsules for the electrophoreticdisplays, wherein the microcapsules include the shell and the dispersionthat is capsuled in the shell, wherein the dispersion includes thesolvent and the electrophoretic fine particles that are dispersed in thesolvent; with the microcapsule composition being characterized by: beinga product as obtained without involving the step of drying themicrocapsules; and having a microcapsule content of 30 to 80 weight %.

The microcapsules for the electrophoretic displays, as referred to inthe present invention microcapsule composition, may be conventional andpublicly known microcapsules for the electrophoretic displays if themicrocapsules are products as obtained without involving the step ofdrying the microcapsules. There is no especial limitation on such as:from what material, by what production process, and via what isproduction steps the microcapsules are products as obtained. Inaddition, the microcapsules may appropriately be processed by such asthe classification treatment when the occasion demands in considerationof purposes of their use. The microcapsules are favorably themicrocapsules for the electrophoretic displays in the microcapsulecomposition as obtained by the present invention production process.That is to say, the present invention microcapsule composition isfavorably the microcapsule composition as obtained by the presentinvention production process.

Although there is no especial limitation on the aqueous medium asreferred to in the present invention composition, specifically the sameas the aqueous mediums used in the present invention production processare favorable.

The present invention composition can appropriately further compriseother components besides the aqueous medium and the microcapsules forthe electrophoretic displays when the occasion demands.

The present invention microcapsule composition is characterized byhaving a microcapsule content of 30 to 80 weight %, more favorably 35 to80 weight %, still more favorably 40 to 80 weight %, of the entirecomposition. In the case where the above content is less than 30 weight%, there is a possibility that: when the composition is formed into apaint, the microcapsule concentration may become so low that themicrocapsules are difficult to arrange in a layer densely by the side ofeach other on a surface to be coated, thus resulting in occurrence ofspaces to cause a lack of displaying and therefore to cause the loweringof the contrast and the image defect (displaying defect). In addition,in the case where the above content is more than 80 weight %, there is apossibility such that: the microcapsules may mutually aggregate to causeproblems in the dispersibility when the composition is formed into apaint; or the image defect (displaying defect) may be caused in the casewhere the microcapsules cannot sufficiently be dispersed; or, if themicrocapsules are strongly dispersed, they may be damaged so much thatthe electrophoretic fine particle dispersion leaks from inside themicrocapsules due to the pressure as applied by laminating an electrodefilm to be a counter electrode. Because of these problems, the resultantelectrophoretic displays cannot sufficiently obtain the contrast, andhave a lot of image defects (displaying defects).

In the present invention microcapsule composition, it is favorable thatthe microcapsules in the composition have a volume-average particlediameter of 30 to 150 μm and a particle diameter distribution by volumesuch that: not less than 80 volume % of the microcapsules are presentwithin the particle diameter range of +40% of the maximum-peak particlediameter (particle diameter corresponding to the maximum peak in theparticle diameter frequency distribution by particle volume) around themaximum-peak particle diameter.

The above volume-average particle diameter is more favorably in therange of 50 to 150 μm. In the case where this volume-average particlediameter is smaller than 30 μm, there is a possibility that there cannotbe obtained electrophoretic displays having a sufficient contrast. Inthe case where the volume-average particle diameter is larger than 150μm, there is a possibility that there may occur problems in the strengthof the microcapsules.

The above particle diameter distribution by volume is favorably aparticle diameter distribution such that: not less than 80 volume %(more favorably not less than 85 volume %) of the microcapsules arepresent within the particle diameter range of “a particle diameterlength corresponding to +40% of the maximum-peak particle diameter”around the maximum-peak particle diameter in the particle diameterfrequency distribution by particle volume. In the case where the aboveratio is less than 80 volume %, there is a possibility that: when thecomposition is formed into a paint and then coated, the microcapsulesmay be coated not in a layer but partially in a multilayer including atleast two layers.

In the present invention microcapsule composition, the total content ofthe microcapsules and the aqueous medium in the composition is favorablynot less than 90 weight %, more favorably not less than 93 weight %,still more favorably not less than 95 weight %, particularly favorablynot less than 98 weight %. In the case where the above content is lessthan 90 weight %, there is a possibility that the effects of the presentinvention cannot be displayed sufficiently when the composition isprovided to the electrophoretic displays.

In the case where the present invention microcapsule composition is(either as it is or after having been mixed with such as the binder) putto use for the electrophoretic displays, there can be produced theelectrophoretic displays that are excellent in various performances(e.g. longtime stability of displaying, respondability, and number oftimes of display rewritability) and exhibit excellent performancesparticularly in such as contrast and image vividness. In the case wherethe electrophoretic displays are produced from the present inventionmicrocapsule composition, for example, there can favorably be cited amethod that involves the steps of: coating the above composition (eitheras it is or after having mixed it with such as the binder) onto such asa film having a transparent electrode; and thereafter laminating anotherfilm onto the resultant coated surface as provided with themicrocapsules. In the case where the above-mentioned microcapsulecomposition is used in this method, the above coating liquid can be madeto have moderate thixotropy in viscosity, and the above coated surfacecan be made to be a coated surface which has little unevenness and is sohomogeneous as to be decreased also in localization and aggregation ofthe microcapsule particles.

As an example of favorable usage of the present invention microcapsulecomposition, there can be cited the production process for a sheet forthe electrophoretic displays. Specifically, this process comprises thesteps of: preparing a coating liquid containing the present inventionmicrocapsule composition in a specific ratio; and then coating theprepared coating liquid onto a substrate; and then drying the resultantcoating film, thereby producing the sheet for the electrophoreticdisplays.

That is to say, the present invention production process for the sheetfor the electrophoretic displays (which may hereinafter be referred toas the present invention production process for the sheet) comprises thesteps of: coating a coating liquid containing a microcapsule compositionfor the electrophoretic displays; and drying the resultant coating film;thereby producing the sheet for the electrophoretic displays; with theproduction process being characterized by: using, as the composition,the present invention microcapsule composition for the electrophoreticdisplays; and further comprising the step of preparing the coatingliquid by mixing the composition in such an amount that the coatingliquid will have a microcapsule content of 25 to 65 weight %.

In the present invention production process for the sheet, there isfirst prepared the coating liquid containing the present inventionmicrocapsule composition for the electrophoretic displays. Specifically,the coating liquid is prepared, if necessary, by adding such as abinder, an additive, and an aqueous medium (e.g. aqueous medium fordilution) to the present invention microcapsule composition for theelectrophoretic displays.

Examples of the aforementioned binder include water-soluble type bindersand emulsion type binders.

Examples of the water-soluble type binders include water-soluble alkydresins, water-soluble acrylic-modified alkyd resins, water-solubleoil-free alkyd resins (water-soluble polyester resins), water-solubleacrylic resins, water-soluble epoxy ester resins, and water-solublemelamine resins.

Examples of the emulsion type binders include alkyl(meth)acrylatecopolymer dispersions, vinyl acetate resin emulsions, vinyl acetatecopolymer resin emulsions, ethylene-vinyl acetate copolymer resinemulsions, acrylate ester (co)polymer resin emulsions, styrene-acrylateester copolymer resin emulsions, epoxy resin emulsions, urethane resinemulsions, acrylic-silicone emulsions, and fluororesin emulsions.

Examples of the aforementioned additive include viscosity-adjustingagents (thickeners), dispersants/wetting agents, defoamers, andmildew-proofing agents/antiseptics. In the case where the coating liquidcontains these additives, there is no especial limitation on theircontents if they are in such a range that there can be obtained acoating liquid having desirable performances.

Examples of the viscosity-adjusting agents (thickeners) include:cellulosic viscosity-adjusting agents (thickeners), such ascarboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose;polycarboxylic viscosity-adjusting agents (thickeners), such aspoly(sodium acrylate), alkaline-soluble emulsions, and associated typealkaline-soluble emulsions; polyethylene-glycolic viscosity-adjustingagents (thickeners), such as polyethylene glycol, polyethylene glycolalkyl ethers, polyethylene glycol alkyl esters, and associated typepolyethylene glycol derivatives; other water-soluble polymers such aspolyvinyl alcohol; and smectite type viscosity-adjusting agents(thickeners), such as montmorillonite, hectorite, and saponite. Thesecan be used either alone respectively or in combinations with eachother.

Examples of the dispersants/wetting agents include: poly(acrylate salts)and styrene-maleic acid copolymer salts; formalin condensation productsfrom naphthalenesulfonate salts; long-chain-alkyl organic sulfonatesalts; polyphosphate salts; long-chain-alkylamine salts; poly(alkyleneoxides); polyoxyalkylene alkyl ethers; sorbitan fatty acid esters;fluorosurfactants, such as perfluoroalkyl-group-containing salts,perfluoroalkyl-group-containing esters, andperfluoroalkyl-group-containing oligomers; acetylenediol; and acetyleneglycol. These can be used either alone respectively or in combinationswith each other.

Examples of the defoamers include siliconic defoamers, pluronic typedefoamers, mineral oil type defoamers, polyesteric defoamers andpolyetheric defoamers. These can be used either alone respectively or incombinations with each other.

Examples of the mildew-proofing agents/antiseptics include organicnitrogen-sulfur compounds, organic nitrogen-halogen compounds,hexadienoic acid chloride salts, cresolic compounds, brominatedcompounds, aldehydic compounds, benzimidazolic compounds, halogenatedcyclic sulfur compounds, organic arsenic compounds, organic coppercompounds, chloroisothiazolone, and isothiazolone. These can be usedeither alone respectively or in combinations with each other.

As to the coating liquid as referred to in the present invention, it isfavorable to uniformly disperse the microcapsules into the coatingliquid in order to obtain a coating film in which the microcapsules areuniformly present. Examples of its means include addition of such as thedispersants/wetting agents and the viscosity-adjusting agents(thickeners), which are cited above as examples of the aforementionedadditives.

Examples of the aforementioned aqueous medium include the same aqueousmediums as mentioned above.

When the aforementioned coating liquid is prepared, the aforementionedcomposition is mixed in such an amount that the coating liquid will havea microcapsule content of 25 to 65 weight %, favorably 30 to 60 weight%, more favorably 30 to 55 weight %, still more favorably 35 to 50weight %. In the case where the coating liquid has a microcapsulecontent of less than 25 weight %, there is a possibility that: themicrocapsule concentration may become so low that the microcapsules aredifficult to arrange in a layer densely by the side of each other on asurface to be coated, thus resulting in occurrence of spaces to cause alack of displaying and therefore to cause the lowering of the contrastand the image defect (displaying defect). In addition, in the case wherethe coating liquid has a microcapsule content of more than 65 weight %,there is a possibility such that: the microcapsules may mutuallyaggregate to cause problems in the dispersibility in the coating liquid;or the image defect (displaying defect) may be caused in the case wherethe microcapsules cannot sufficiently be dispersed; or, if themicrocapsules are strongly dispersed, they may be damaged so much thatthe electrophoretic fine particle dispersion leaks from inside themicrocapsules due to the pressure as applied by laminating an electrodefilm to be a counter electrode. Because of these problems, the resultantelectrophoretic displays cannot sufficiently obtain the contrast, andhave a lot of image defects (displaying defects).

In the present invention production process for the sheet, subsequently,the prepared coating liquid is coated onto the substrate and then dried,thereby producing the sheet for the electrophoretic displays.

Examples of the aforementioned substrate include transparent conductivefilms (e.g. PET films with ITO), films having a conductive layer (e.g.copper-laminated polyimide films), and films as coated with metal foils(e.g. aluminum foil) or conductive polymers (e.g. polyacetylene,polyaniline, and polypyrrole).

There is no especial limitation on the method for coating the coatingliquid onto the substrate, and the coating liquid may be coated byhitherto publicly known methods.

There is no especial limitation on the conditions of the aforementioneddrying step. However, the drying step may be carried out in thetemperature range of favorably 15 to 150° C. (more favorably 20 to 120°C.) for favorably 1 to 60 minutes (more favorably 5 to 45 minutes).

The present invention handling method for the microcapsules for theelectrophoretic displays (which may hereinafter be referred to as thepresent invention handling method) is a handling method for themicrocapsules including the shell and the dispersion that is capsuled inthe shell, wherein the dispersion includes the solvent and theelectrophoretic fine particles that are dispersed in the solvent, inwhich handling method the microcapsules are handled by custody,preservation, transportation, and other various handling in the form ofthe microcapsule composition such that: the microcapsules are present inthe aqueous medium; and the microcapsule composition has a microcapsulecontent of 30 to 80 weight %.

The microcapsules for the electrophoretic displays, as handled by thepresent invention handling method, will do if the microcapsules areconventional and publicly known microcapsules for the electrophoreticdisplays. There is no especial limitation on such as: from whatmaterial, by what production process, and via what production steps themicrocapsules are products as obtained. In addition, the microcapsulesmay appropriately be processed by such as the classification treatmentwhen the occasion demands in consideration of purposes of their use.Specifically, for example, microcapsules for the electrophoreticdisplays, which are obtained by once being prepared by microcapsulationand thereafter being isolated and then being dried and then beingclassified in a dry manner, can also be used as the microcapsules (asreferred to in the present invention handling method) for theelectrophoretic displays. However, the microcapsules are favorably themicrocapsules for the electrophoretic displays in the microcapsulecomposition as obtained by the above present invention productionprocess.

Examples of the handling, as referred to in the present invention,include packing into containers, repacking between containers, andmeasuring besides the above-mentioned custody, preservation, andtransportation.

Although there is no especial limitation on the aqueous medium asreferred to in the present invention handling method, specifically thesame as the aqueous mediums used in the above present inventionproduction process are favorable.

In the present invention handling method, the microcapsules for theelectrophoretic displays are handled in the presence of the aqueousmedium. However, other components can appropriately be used besides theaqueous medium when the occasion demands.

In addition, in the present invention handling method, the microcapsulesare handled in the form of the microcapsule composition having amicrocapsule content of 30 to 80 weight % of the entire compositionincluding such as the aqueous medium as well. However, the above contentis more favorably in the range of 35 to 80 weight %, still morefavorably 40 to 80 weight %. In the case where the above content is lessthan 30 weight %, there is a possibility that: when the composition isformed into a paint, the microcapsule concentration may become so lowthat the microcapsules are difficult to arrange in a layer densely bythe side of each other on a surface to be coated, thus resulting inoccurrence of spaces to cause a lack of displaying and therefore tocause the lowering of the contrast and the image defect (displayingdefect). In addition, in the case where the above content is more than80 weight %, there is a possibility such that: the microcapsules maymutually aggregate to cause problems in the dispersibility when thecomposition is formed into a paint; or the image defect (displayingdefect) may be caused in the case where the microcapsules cannotsufficiently be dispersed; or, if the microcapsules are stronglydispersed, they may be damaged so much that the electrophoretic fineparticle dispersion leaks from inside the microcapsules due to thepressure as applied by laminating an electrode film to be a counterelectrode. Because of these problems, the resultant electrophoreticdisplays cannot sufficiently obtain the contrast, and have a lot ofimage defects (displaying defects).

EFFECTS AND ADVANTAGES OF THE INVENTION

The present invention can provide: a microcapsule composition forelectrophoretic displays; a production process for the microcapsulecomposition for the electrophoretic displays; a production process for asheet for the electrophoretic displays; and a handling method formicrocapsules for the electrophoretic displays; wherein the microcapsulecomposition contains microcapsules and, when used for theelectrophoretic displays, can make them as excellent as conventional invarious performances (e.g. longtime stability of displaying,respondability of displaying, contrast, and number of times of displayrewritability) and, particularly above all, can make the electrophoreticdisplays exhibit a very high performance as to the contrast.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is more specifically illustrated bythe following examples of some preferred embodiments in comparison withcomparative examples not according to the present invention. However,the present invention is not limited to these examples in any way.Incidentally, for the sake of convenience, the units “part(s) by weight”and “liter(s)” may hereinafter be abbreviated simply to “part(s)” and“L” respectively.

Example 1

A four-necked flask of 500 mL was charged with 30 g of titanium oxide(produced by Ishihara Sangyo Kaisha, Ltd., trade name: Tipaque CR-97),261 g of dodecylbenzene, and 2 g of titanate coupling agent (produced byAjinomoto Co., Inc., trade name: Plemact TTS), and then these materialswere mixed by stirring. Thereafter, the flask was put into an ultrasonicbath (produced by Yamato Co., Ltd., product name: BRANSON 5210) of 55°C., and then the contents of the flask were subjected to aultrasonically dispersing treatment under stirred conditions for 2hours, thus obtaining a titanium oxide dispersion (I).

The particle diameters of the titanium oxide in the above dispersion (1)were measured. As a result, the volume-average particle diameter was0.34 μm. The particle diameter distribution was measured with a Shimadzucentrifugal-sedimentation-type particle diameter distributionmeasurement apparatus SA-CP3 (produced by Shimadzu Corporation).

Into this dispersion (1), 6 g of anthraquinone blue oil dye wasdissolved, thus obtaining a blue-colored dispersion (1) forelectrophoretic displays.

Under stirring with a disper (produced by Tokushu Kika Kogyo Co., Ltd.,product name: ROBOMICS), 105 g of the dispersion (1) for electrophoreticdisplays as heated to 55° C. was added to an aqueous solution which hadbeforehand been prepared by dissolving 5.5 g of gum arabic and 5.5 g ofgelatin into 60 g of water and then maintained at 43° C. The stirringspeed was gradually raised to stir the resultant mixture at 1,050 r.p.m.for 60 minutes, thus obtaining a suspension.

While 300 mL of warm water of 43° C. was added to this suspension, thestirring speed was gradually lowered to 500 r.p.m. Furthermore, 0.75 mLof 10% aqueous NaCO₃ solution was added thereto, and thereafter theresultant mixture was maintained for 30 minutes. Then, 11 mL of 10%acetic acid solution was added thereto at a constant rate over a periodof 25 minutes, and then the resultant mixture was cooled to not higherthan 10° C.

The mixture was maintained in the cooled state for 2 hours, and then 3mL of 37% formalin solution was added thereto at a constant rate in 30seconds, and then 22 mL of 10% aqueous NaCO₃ solution was further addedthereto at a constant rate over a period of 25 minutes.

The resultant mixture was cooled to ordinary temperature under stirredconditions and then aged for 20 hours, thus preparing microcapsules (1)and further obtaining a microcapsule dispersion (1). The microcapsules(1) included a shell and the aforementioned dispersion (1) forelectrophoretic displays that was capsuled in the shell. In themicrocapsule dispersion (1), the above microcapsules (1) were dispersed.

At that point of time, the particle diameters of the microcapsules (1)were measured with a laser-diffraction/scattering typeparticle-diameter-distribution measurement apparatus, HORIBA LA-910(produced by Horiba Seisakusho Co., Ltd.). As a result, thevolume-average particle diameter was 67 μm.

The microcapsule dispersion (1) as obtained was diluted with 1,500 g ofwater to which 1.25 mL of 10% aqueous NaCO₃ solution had been added. Theresultant dilution was passed through a mesh sieve having a mesh openingsize of 85 μm, and then placed into a separatory funnel, and then leftstationary. Then, 7 hours later, the lower liquid of the separated upperand lower liquids was extracted. To the residual upper liquid, there wasadded 1,500 g of water to which 1.25 mL of 10% aqueous NaCO₃ solutionhad been added. These materials were uniformly mixed by hand shaking tothereby carry out re-dispersion, and thereafter left stationary. Asequence of the above operations of the stationary leaving, theextraction of the lower liquid, and the re-dispersion of the upperliquid were repeated three times, thus completing the wetclassification.

The microcapsule dispersion (1) which had been subjected to the abovewet classification was concentrated by suction filtration, thusobtaining a microcapsule composition (1) as a filtrated cake includingthe classified microcapsules (1). The classified microcapsules (1) had avolume-average particle diameter of 74.6 μm and the maximum-peakparticle diameter of 77.2 μm (incidentally, the above maximum-peakparticle diameter is a particle diameter corresponding to the maximumpeak in the particle diameter distribution by volume; the samedefinition is hereinafter applied). In addition, the particle diameterdistribution by volume was such that: 85 volume % of the microcapsuleswere present within the particle diameter range of ±40% of themaximum-peak particle diameter around the maximum-peak particlediameter. Furthermore, the microcapsules (1) were present at a contentof 45 weight % in the above microcapsule composition (1). These resultsare listed in Table 1.

Example 2

A titanium oxide dispersion (2) was obtained by the same procedure as ofExample 1 except to replace the dodecylbenzene with Highsol SA296(produced by Nisseki Kagaku Co., Ltd.).

The particle diameters of the titanium oxide in the above dispersion (2)were measured in the same way as of Example 1. As a result, thevolume-average particle diameter was 0.27 μm.

Into this dispersion (2), 6 g of anthraquinone blue oil dye wasdissolved, thus obtaining a blue-colored dispersion (2) forelectrophoretic displays.

Thereafter, the same procedure as of Example 1 was carried out exceptthat: the dispersion (2) for electrophoretic displays was used insteadof the dispersion (1) for electrophoretic displays, and the stirringwith the diaper at 1,050 r.p.m. for 60 minutes was changed to thestirring at 800 r.p.m. for 60 minutes. Thereby, microcapsules (2) wereprepared, and further a microcapsule dispersion (2) was obtained. Themicrocapsules (2) included a shell and the aforementioned dispersion (2)for electrophoretic displays that was capsuled in the shell. In themicrocapsule dispersion (2), the above microcapsules (2) were dispersed.

At that point of time, the particle diameters of the microcapsules (2)were measured in the same way as of Example 1. As a result, thevolume-average particle diameter was 105 μm.

The microcapsule dispersion (2) as obtained was diluted with 1,500 g ofwater to which 1.25 mL of 10% aqueous NaCO₃ solution had been added. Theresultant dilution was passed through a mesh sieve having a mesh openingsize of 130 μm. Thereafter, microcapsules having particle diameters ofnot larger than 70 μm were removed with a continuous wet classificationapparatus, Sanitary Cyclone (produced by Nippo Co., Ltd.).

The microcapsule dispersion (2) which had been subjected to the abovewet classification was concentrated by suction filtration, thusobtaining a microcapsule composition (2) as a filtrated cake includingthe classified microcapsules (2). The classified microcapsules (2) had avolume-average particle diameter of 113.2 μm and the maximum-peakparticle diameter of 118.7 μm. In addition, the particle diameterdistribution by volume was such that: 81 volume % of the microcapsuleswere present within the particle diameter range of ±40% of themaximum-peak particle diameter around the maximum-peak particlediameter. Furthermore, the microcapsules (2) were present at a contentof 58 weight % in the above microcapsule composition (2). These resultsare listed in Table 1.

Example 3

In the same way as of Example 1, microcapsules (3) were prepared, andfurther a microcapsule dispersion (3) was obtained. In the microcapsuledispersion (3), the above microcapsules (3) were dispersed.

At that point of time, the particle diameters of the microcapsules (3)were measured in the same way as of Example 1. As a result, thevolume-average particle diameter was 65 μm.

The microcapsule dispersion (3) as obtained was subjected to wetclassification in the same way as of Example 1.

The microcapsule dispersion (3) which had been subjected to the abovewet classification was concentrated by suction filtration in the sameway as of Example 1 except that the suction amount was reduced. Thus,there was obtained a microcapsule composition (3) as a filtrated cakeincluding the classified microcapsules (3). The classified microcapsules(3) had a volume-average particle diameter of 70.7 μm and themaximum-peak particle diameter of 75.5 μm. In addition, the particlediameter distribution by volume was such that: 88 volume % of themicrocapsules were present within the particle diameter range of ±40% ofthe maximum-peak particle diameter around the maximum-peak particlediameter. Furthermore, the microcapsules (3) were present at a contentof 33 weight % in the above microcapsule composition (3). These resultsare listed in Table 1.

Example 4

In the same way as of Example 2, microcapsules (4) were prepared, andfurther a microcapsule dispersion (4) was obtained. In the microcapsuledispersion (4), the above microcapsules (4) were dispersed.

At that point of time, the particle diameters of the microcapsules (4)were measured in the same way as of Example 2. As a result, thevolume-average particle diameter was 112 μm.

The microcapsule dispersion (4) as obtained was subjected to wetclassification in the same way as of Example 2 except that: there wasused a mesh having a mesh opening size of 140 μm, and microcapsuleshaving particle diameters of not larger than 80 μm were removed.

The microcapsule dispersion (4) which had been subjected to the abovewet classification was concentrated by suction filtration in the sameway as of Example 2 except that the suction amount was increased. Thus,there was obtained a microcapsule composition (4) as a filtrated cakeincluding the classified microcapsules (4). The classified microcapsules(4) had a volume-average particle diameter of 121.8 μm and themaximum-peak particle diameter of 128.1 μm. In addition, the particlediameter distribution by volume was such that: 80 volume % of themicrocapsules were present within the particle diameter range of +40% ofthe maximum-peak particle diameter around the maximum-peak particlediameter. Furthermore, the microcapsules (4) were present at a contentof 75 weight % in the above microcapsule composition (4). These resultsare listed in Table 1.

Comparative Example 1

In the same way as of Example 1, microcapsules (c1) were prepared, andfurther a microcapsule dispersion (c1) was obtained. In the microcapsuledispersion (c1), the above microcapsules (c1) were dispersed.

At that point of time, the particle diameters of the microcapsules (c1)were measured in the same way as of Example 1. As a result, thevolume-average particle diameter was 67 μm, and the maximum-peakparticle diameter was 65.1 μm. In addition, the particle diameterdistribution by volume was such that: 51 volume % of the microcapsuleswere present within the particle diameter range of ±40% of themaximum-peak particle diameter around the maximum-peak particlediameter.

The microcapsule dispersion (c1) as obtained was filtrated and thendried, thus obtaining a powder of the microcapsules (c1). These resultsare listed in Table 1.

Comparative Example 2

The powder of the microcapsules (c1) as obtained in Comparative Example1 was passed through a mesh having a mesh opening size of 85 μm, thusobtaining microcapsules (c2) of Comparative Example 2. In the aboveoperation of passing the powder through the mesh having a mesh openingsize of 85 μm, aggregates remaining on the mesh were seen in a largeamount.

The amount of the powder of the microcapsules (c2) as obtained throughthe mesh was 31 weight % of the entire powder of the microcapsules (c1).

The particle diameters of the microcapsules (c2) were measured in thesame way as of Example 1. As a result, the volume-average particlediameter was 67 μm, and the maximum-peak particle diameter was 61.9 μm.In addition, the particle diameter distribution by volume was such that:53 volume % of the microcapsules were present within the particlediameter range of ±40% of the maximum-peak particle diameter around themaximum-peak particle diameter. These results are listed in Table 1.

Electrophoretic displays (1) to (4), (c1), and (c2) were produced in thefollowing procedure from the microcapsule compositions (1) to (4) andpowdery microcapsules (c1) and (c2), respectively, as obtained in theabove ways.

First of all, a coating liquid was prepared as follows. Any one of themicrocapsule compositions (1) to (4) or the powdery microcapsules (c1)or (c2) were mixed with an acrylic emulsion for binders (solid componentconcentration: 45 weight %) in such an amount that the weight ratio ofmicrocapsules/acrylic emulsion for binders would be as listed in Table2. Water was further added to the resultant mixture in such an amountthat the microcapsule content in the coating liquid would be as listedin Table 2. Thus, coating liquids (1) to (4), (c1), and (c2) wereprepared.

Next, the prepared coating liquid was coated onto an ITO-having PET filmwith an applicator and thereafter dried at 90° C. for 10 minutes, thuspreparing a coated sheet (sheet for electrophoretic displays).Subsequently, another ITO-having film was piled and thereby laminatedonto the coated side of this coated sheet, thus obtaining anelectrophoretic display as equipped with counter electrodes.

The case where the microcapsule content is too low in the microcapsulecomposition results inevitably in a low solid component concentration ofthe coating liquid, also. Accompanying it, the viscosity of the coatingliquid also decreases so much that the leveling ability is deterioratedwhen the coating liquid is coated. In addition, the resultant coatingfilm is also so thin that spaces between the microcapsules are opened sowide that the microcapsules fall into a “sparse” state. Dense existenceof the microcapsules on the coated surface enhances the displayingproperties and remarkably acts upon the contrast above all.

As to each of the electrophoretic displays (1) to (4), (c1), and (c2) asobtained, a direct current voltage of 30 V was applied between bothelectrodes for 1 second, and thereafter the contrast was measured. As tothe contrast, the reflectances of blue and white displays were measuredwith a Macbeth spectrophotometric densitometer, SpectroEye (produced byGretag Macbeth), and the contrast was represented by the ratio(contrast) between these reflectances (ratio (contrast) betweenreflectances=white reflectance/blue reflectance). Incidentally, theratio between reflectances is a value as obtained by: measuring areflectance of a display (e.g. blue) when the direct current voltage isapplied between the counter electrodes of the electrophoretic display;and subsequently measuring a reflectance of a display (e.g. white) whenthe polarity is reversed to apply the direct current voltage; and thencalculating the ratio between both reflectances. It is hereuponprescribed that the reflectance should be measured as to one entire faceof the electrophoretic display.

In addition, the coated surface was optically magnified with amicroscope (produced by Highlocks Co., Ltd., product name: Power HighScope KH-2700) to observe and evaluate a state of rows of themicrocapsules and a damaged or defective (non-electrophoretic) state ofthe microcapsules on the following standards.

Their results are listed in Table 1.

(State of Rows of Microcapsules):

⊚: The microcapsules are densely packed without spaces, and there isalso little overlap between the microcapsules, and there are noaggregates.

∘: The microcapsules are in a dense state as a whole, but there are some“sparse” portions. There are also some overlap portions between themicrocapsules, but there are no aggregates.

Δ: There are also dense portions, but there are also considerably many“sparse” portions. There is little overlap between the microcapsules,but aggregates are seen.

x: The microcapsules are sparse, and there are few dense portions. Thereare also considerably many aggregates.

(Damage or Defect (Non-Electrophoresis) of Microcapsules):

There was counted the number of damaged or defective(non-electrophoretic) microcapsules existing in any five visual fields(200 to 400 microcapsules existed per one visual field) under 200magnifications.

TABLE 1 Volume- Maximum - Ratio of microcapsules average peak presentwithin particle Ratio Number of Microcapsule particle particle diameterrange of ±40% (contrast) damaged or content diameter diameter ofmaximum-peak particle between State of rows defective (wt %) (μm) (μm)diameter around it (vol. %) reflectances of microcapsules microcapsulesExample 1 45 74.6 77.2 85 5.6 ⊚ 6 Example 2 68 113.2 118.7 81 7.2 ⊚ 8Example 3 33 70.7 75.5 88 4.7 ◯ 13 Example 4 75 121.8 128.1 80 6.9 ◯ 11Comparative 100 62.1 65.1 51 2.1 X 36 Example 1 Comparative 100 60.361.9 53 2.8 Δ 28 Example 2

TABLE 2 Microcapsules/ Microcapsule acrylic emulsion content inMicrocapsules for binders coating liquid used (weight ratio) (weight %)Coating liquid Microcapsule 10/2 40 (1) Composition (1) Coating liquidMicrocapsule 10/4 45 (2) Composition (2) Coating liquid Microcapsule10/0.5 30 (3) Composition (3) Coating liquid Microcapsule 10/1 60 (4)Composition (4) Coating liquid Microcapsule 10/4 50 (c1) Composition(c1) Coating liquid Microcapsule 10/4 40 (c2) Composition (c2)

Various details of the invention may be changed without departing fromits spirit not its scope. Furthermore, the foregoing description of thepreferred embodiments according to the present invention is provided forthe purpose of illustration only, and not for the purpose of limitingthe invention as defined by the appended claims and their equivalents.

1. A production process for a microcapsule composition forelectrophoretic displays, wherein the microcapsule composition includesan aqueous medium and microcapsules for the electrophoretic displays,wherein the microcapsules include a shell and an electrophoretic fineparticle dispersion that is capsuled in the shell, wherein theelectrophoretic fine particle dispersion includes a solvent andelectrophoretic fine particles that are dispersed in the solvent; withthe production process comprising: a dispersing step of dispersing theelectrophoretic fine particles into the solvent to obtain theelectrophoretic fine particle dispersion; a microcapsuling step ofcapsuling the electrophoretic fine particle dispersion into the shell inthe presence of the aqueous medium, thereby obtaining a preparationliquid including the microcapsules and the aqueous medium, thepreparation liquid having a microcapsule concentration of not more than15 weight %, a wet classification step of treating the preparationliquid to classify the microcapsules, and a concentration step ofreducing the aqueous medium from a dispersion resultant from theclassification step, thereby concentrating the dispersion and formingthe microcapsule composition, wherein: the composition having amicrocapsule content of 30 to 80 weight % is obtained without involvingthe step of drying the microcapsules.
 2. The production process of claim1, wherein the microcapsules have a shell thickness in the range of 0.1to 5 μm.
 3. The production process of claim 1, wherein the microcapsuleshave a volume-average particle diameter of 30 to 150 μm and not lessthan 80% by volume of the microcapsules being present within theparticle diameter range of ±40% of the maximum-peak particle diameteraround the maximum-peak particle diameter.